Many processes which have been invented require reliable data on a particular aspect of the process before the process receives validation of its efficacy from either a regulatory body or industry. Often, methods to obtain the reliable data are beyond the scope of the current art, thereby rendering beneficial processes commercially unusable. For example, there is currently no method to provide reliable data for the residence time of an object undergoing analysis in the situation where the object is a constituent of a heterogeneous phase throughput system. This has rendered many beneficial processes which rely on such data unusable. An example of such a process is an aseptic process for the production of a low acid shelf-stable food.
Before distribution to consumers, low acid (pH over 4.6) shelf-stable food products must be sterilized through heat treatment or other processes in order to achieve microbiological inactivation in the food product. An example of the sterilization of a heterogeneous food (foods having different phase constituents) is the heat treatment process for canned soups having food (vegetable and/or meat) particulates. The soup is dispensed into the cans and hermetically sealed therein. The cans are then placed upon a rotator and heated to a temperature of approximately 121.degree. C. while rotating. The heat process is necessary to achieve adequate microbiological inactivation to produce a shelf-stable product. The rotation of the cans expedites the heating of the liquid medium and the exterior of the solid particulates. However, the heating of the center of the food particulates is a much slower process because it can only take place through conduction heating. The heating time for the center of the food particulate increases as the aspect ratio (width to thickness) for the food particulate decreases. Thus, it will take longer to heat the center of a potato cube than it will to heat the center of a green bean (which has a quasi-cylindrical shape) because the surface area to volume of the green bean is greater than the surface area to volume of the potato cube.
An alternative microbiological inactivation process for food particulates in a liquid medium is aseptic processing. In aseptic processing, the heterogeneous food is conveyed through a number of first heat exchange sections for heating, to a holding tube for a set residence time to sterilize the food particulates, then to a number of second heat exchange sections for cooling before packaging. The thermal process design for such a product requires the use of a mathematical model which requires the residence time distribution data to optimize the product quality and microbial safety. This process is much faster than the latter, however, it has been difficult to establish the residence time for the food particulates because present tracking methods of the food particulates are unreliable. In order to insure that a safe lethality level for microorganisms is obtained for the center of food particulates, the residence time for food particulates in the holding tube and at the heat exchangers at a predetermined temperature must be established with reliable data. Although microbiological validation may be conducted on a batch of the heterogeneous food at the end of the validation process, without reliable data on the residence time of food particulates in the holding tube a safe lethality level will remain unknown or unsure at best. Therefore, governmental and industry regulatory bodies will not accept the safety of such a process which results in the inability to use this process to sterilize heterogeneous foods for sale to the public.
The food industry has invested a tremendous amount of time and money in analyzing this process and trying to provide reliable data for the residence time for food particulates undergoing this process. From the analysis of this process, much has been learned and accepted as fact. First, there is a definite difference between the residence time distribution of the food particulates and the liquid medium, with the particulates, on average, traveling faster than the mean velocity of the heterogeneous food. The size and concentration of the particulates affect the residence time as do the flow rate and viscosity of the heterogeneous food. The residence time must be measured for the fastest food particulates to ensure microbiological inactivation. With this knowledge, some in the food industry have attempted to measure the residence time of the food particulates or otherwise verify the efficacy of this process.
One such method uses magnetic resonance imaging to create temperature maps of food particulates to verify that the center is properly heated. Other methods place tracers in the actual food particulates and attempt to calculate the residence time by tracking the tracers. However, the size, shape, density and rotational inertia of the food particulate are altered by placing tracers in the actual food particulate. This results in unreliable data because that which is being tracked flows differently, and thus has a different residence time from the actual food particulate. Also, breakage of the particulate may occur resulting in the tracer slipping out of the particulate which would also effect the data.
Therefore, industry has yet to provide a reliable method for verifying the residence time of an object undergoing analysis in a situation where the object is a constituent of a heterogeneous phase system. The absence of such a method has prevented the use of various processes which need reliable data on the residence time of the object to demonstrate their efficacy.